In production and processing flows in various industries, measurement operations are essential, and measurement accuracy directly affects levels of the entire flows. In some cases, if there is a large offset in a measurement result, it may directly lead to processed products or produced equipment scrapped, thereby resulting in huge losses.
For example, in the Thin Film Transistor-Liquid Crystal Display (TFT-LCD) industry, in a process of production of a liquid crystal panel, it is one of the important flows to grind a glass chip, which achieves the effect of removing foreign matters on upper and lower surfaces of the panel by using a grinding head to drive a grinding belt to rotate directionally. A grinding effect directly determines the yield of the entire production process, and is largely determined by a size of a grinding clearance. For liquid crystal panels with different thicknesses, grinding clearances which are used are often different. Therefore, it needs to select a size of the grinding clearance according to a thickness of a liquid crystal panel before grinding, which requires accurate measurement of the grinding clearance. In the conventional method for measuring a grinding clearance, the grinding clearance is measured by an operator using a feeler. Because of an error caused by the feeler itself and an error manually caused by the operator, the measurement method may result in a large error and a long time delay, which are not beneficial to the product quality and production efficiency of the whole production line.